High-pressure Langmuir probe in a weak flowing plasma or a plasma sheath

Smy, P. R.; Noor, A. I.

doi:10.1063/1.322835

Cited by 25 publications

(14 citation statements)

References 7 publications

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“…Furthermore, the impressive number of publications by Clements and Smy [78,79,82,91,[111][112][113][114][115][116][117] while apparently covering a broad range of experimental conditions, are mostly limited to the study of flame plasmas. These are characterized by electron temperatures varying from 1,500 K to 3,000 K, and in which the electron density does not exceed 10 18 m -3 , some four orders of magnitude below the regimes dealt with in this work, although Smy [84,118], and Smy and Noor [118], mention charge density up to 10 20 -10 23 m -3 . To the author's knowledge, the works dealing with these high values are only Clements and Smy's paper of 1972 [113] and Holmes et al [105].…”

Section: Introductionmentioning

confidence: 69%

“…If E≈V p /δ s and δ s ≈ L(α 2 χ 2 /Re) 1/2 , this condition is satisfied only if Reα 2 <1. This is the sheath convection regime (E2.1 in figure 5.11) although in the analysis by Smy and Noor [118] the limit to sheath convection regimes is expressed including χ. For Reα 2 >1, the field is able to attract to the probe only a fraction of the ions convected to the sheath (E-field convection regime, E2.2 in figure 5.11).…”

Section: Origin Of the Criteriamentioning

confidence: 99%

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A Langmuir multi-probe system for the characterization of atmospheric pressure arc plasmas

Fanara

Richardson

2001

J. Phys. D: Appl. Phys.

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The 'high-pressure' atmospheric (TIG) arc plasma is studied by means of a multi-Langmuir probe system. In order to determine the appropriate regime of operation, definitions of the plasma parameters for the description of the argon arc are considered and evaluations are presented. A description of the probe basic techniques is followed by an in-depth discussion of the different regimes of probe operation. The emphasis is put on atmospheric and flowing (arc) regimes. Probe sheath theories are compared and "Nonidealities" like cooling due to plasma-probe motion and probe emission mechanisms are then described.The extensive literature review reveals that the existing probe theories are inappropriate for a use in the TIG arc, because of 'high' pressure (atmospheric), broad range of ionization across the arc, flowing conditions, and ultimately, to the uncertainty about onset of Local Thermodynamical Equilibrium. The Langmuir probe system is built to operate in floating and biased conditions. The present work represents the first extensive investigation of electrostatic probes in arcs where the experimental difficulties and the primary observed quantities are presented in great detail. Analysis methodologies are introduced and experimental results are presented towards a unified picture of the resulting arc structure by comparison with data from emission spectroscopy. Results from different measurements are presented and comparison is made with data on TIG arcs present in literature. Probe obtained temperatures are lower than the values obtained from emission spectroscopy and this 'cooling' is attributed to electron-ion recombination. However, it is believed that probes can access temperatures regions not attainable by emission spectroscopy. Only axial electric potential and electric field are obtained because of the equipotential-probe requirement. Estimations of the sheath voltage and extension are obtained and a qualitative picture of the ion and electron current densities within the arc is given.on floating and plasma potentials and estimates of the sheath voltage are made, which are then compared with the results of Chapter 4. Chapter 13 deals with further 'electrical' parameters (current densities, electric field and electrical conductivity). In Chapter 14 several experimental results are presented together in order to gain a unified picture of the resulting arc structure and some observations about possible conduction structures within arcs are made. Finally Chapter 15, after a summary of the whole work, reports the conclusions obtained and suggests further investigations.

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Section: Introductionmentioning

confidence: 69%

Section: Origin Of the Criteriamentioning

confidence: 99%

A Langmuir multi-probe system for the characterization of atmospheric pressure arc plasmas

Fanara

Richardson

2001

J. Phys. D: Appl. Phys.

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“…The distribution of the plasma and fields near an electric probe in a drifting plasma were numerical simulated to study the orbital motion of the probe in space [13], [14] and others in which the current versus voltage curve of a biased probe in a drifting plasma were calculated [15], [16]. The physical situation in the previous studies is quite different to our case.…”

Section: Pic Simulation Of the Langmuir Probe Currentmentioning

confidence: 84%

Disturbance of a Langmuir Probe at the Steady-State Sheath Boundary in a Drifting Plasma

Kwok

Bilek

McKenzie

et al. 2004

IEEE Trans. Plasma Sci.

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The disturbance resulting from the presence of a positively biased Langmuir probe at an equilibrium steady-state ion sheath boundary in the drifting plasma is simulated by the twodimensional particle-in-cell (PIC) method in rectangular coordinates. The positive potential of the probe was found to shield electrons on the side of the probe away from the sample surface from the negative potential of the sample surface and thereby cause an increase in the electron current drawn by the probe. The drifting ions on the same side of the probe are slowed by it and thereby raising the ion density in front of the probe. The electron currents of the probe are calculated at different probe positions from the sample surface. It is found that the sheath boundary as defined by the probe current is wider than the unperturbed boundary. The widening of the sheath boundary agrees well with experimental sheath boundary measurements.

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“…The difference in floating potential given by eqn (8), is dependent on the concentration of electrons in the two compartments at the electrode surface (Lw and Rw indicate the left and right wall) and the bulk flame (LN and RN indicate left and right bulk flame).…”

Section: Kinetic Theory: Floating Potentialmentioning

confidence: 99%

“…Calcote and King in the 1950s developed Langmiur probes that have been extensively used for flame diagnostics fuelled by the advancement of jet and rocket propulsion systems. 7,8 These devices are two electrode probes and were used to measure conductivity as a method of measuring total ion and electron concentration and electron temperature.…”

Section: Introductionmentioning

confidence: 99%

Plasma electrochemistry: potential measured at boron doped diamond and platinum in gaseous electrolyte

Hadzifejzovic

Galiani

Caruana

2006

Phys. Chem. Chem. Phys.

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Premixed hydrogen/oxygen flame doped with ionisable alkali metals was considered as a dilute electrolyte. Two identical premixed flames which were in physical contact, served as a two compartment flame electrolyte cell. Five different electrochemical cells were studied, each containing a different combination of three alkali metals, Li, K and Cs. Pairs of boron doped diamond (BDD) and platinum electrodes were used to measure the overall zero current cell potential. The total potential measured across the cell was shown to be the sum of the mixed potential, dependent on the identity of ionised species present in the flame, and the diffusion potential originating at the junction between the two flames. Classical kinetic molecular theory and electrochemical theory of mixed potentials have been applied to account for the potential difference measured across these gas phase electrochemical cells. The relative merits of both models are discussed in the context of the experimental results obtained.

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High-pressure Langmuir probe in a weak flowing plasma or a plasma sheath

Cited by 25 publications

References 7 publications

A Langmuir multi-probe system for the characterization of atmospheric pressure arc plasmas

A Langmuir multi-probe system for the characterization of atmospheric pressure arc plasmas

Disturbance of a Langmuir Probe at the Steady-State Sheath Boundary in a Drifting Plasma

Plasma electrochemistry: potential measured at boron doped diamond and platinum in gaseous electrolyte

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